Apparatus for making prestressed concrete



Nov. 8, 1966 R. R. oAKDEN APPARATUS FOR MAKING PRESTRESSED CONCRETE Filed Aug. 17, 1964 United States Patent() 3,283,385 APPARATUS FOR MAKING PRESTRESSED CONCRETE Richard Ralph Oakden, Ashbourne, England, assigner to Richard Lees Limited, Derby, British company Filed Aug. 17, 1964, Ser. No. 390,088 Claims priority, application Great Britain, Aug. 21,1963, 33,046/ 63 12 Claims. (Cl. 25-118) This invention relates to prestressed concrete and in particular to apparatus for making same.

An object of the present invention is to provide an irnproved means for manufacturing prestressed concrete.

According to the present invention there is provided apparatus for making prestressed concrete comprising a stress bed on to which unhardened concrete is adapted to be fed, means for continuously feeding stressing wire over said bed so as to be surrounded by said concrete and embedded therein when the concrete has hardened, means for continuously applying a wire-tensioning load to said wire whereby the wire is maintained in a tensioned condition, and a xed stress-compensating device included in said load-applying means and through which the wire is fed before passing to a movable member having a constant load applied thereto, said member be slidable relative lto said stress-compensating device under the influence of said load to maint-ain constantly the Wire 'under a given tension so that the reaction induced by the tension in the prestressing wire is transferred by the stress-compensating Mugginton, England, a

-device to act in an opposite direction on the hardened concrete.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which:

FIGURE 1 is a diagrammatic sideelevation of a prestressed concrete forming apparatus,

FIGURE 2 is a detail sectional view on the line II`II of FIGURE l illustrating a stress compensating device as employed in the arrangement of FIGURE 1,

FIGURE 3 is a diagrammatic View showing the disposition lof the capstan members employed in the stress compensating device and FIGURE 4 lis a diagrammatic sectional view of an alternative form of stress compensating device -to that shown in FIGURE 2.

Referring to FIGURES l to 3 of the drawings, appara- A tus for making prestressed concrete comprises a stress bed formed by a horizontal conveyor 5 made up of a plurality of spaced rollers arranged to receive from -a moulding ysection 6 at its forward end a continuous supply of a concrete mixture. The forward end of the conveyor 5 is constituted by an endless belt 7, which is driven at a constant predetermined rate in order to advance the moulded concrete in green form along the conveyor 5. Surrounding the conveyor 5 for a substantial portion of its length is a concrete curing tunnel 8 and positioned above the stress bed at points subsequent to the emergency of the hardened concrete beam 9 from the tunnel 8 is a hardness testing device 10 for testing the hardness of the concrete and 'a dying saw 11 by means of which the Ibeam can be cut into sections as desired. Steel wire 12 for creating the prestressed condition of the final concrete product is fed from a stock coil 13 and is passed over a stress compensating device shown generally at 14 in FIG- URE l before passing through a wire pretreatment tunnel 3,283,385 Patented Nov. 8, 1966 ice 15 located below the conveyor 5. The treatment of the wire in the tunnel 15 consists in heating the wire ata temperature of `l50-200" C. for a period of 7 to 8 hours during which time the tendency of the wire to creep owing to molecular deformation as a result of its being in a tensioned condition is accelerated. On leaving the tunnel 15 the wire 12 passes upwardly around a pulley wheel 16 before extending parallel to and .above the conveyor 5 and at the same time passing through the moulding ysection 6 so that when the moulding section 6 is filled with concrete in green form the wire 12 within this section is surrounded by the concrete.

The pulley 16 is mounted so that its horizontal axis is slidable along a horizontal plane and movement of the axis of the pulley 16 can 'be eiected by -a hydraulic or pneumatic piston and cylinder device 17. By control of the piston and cylinder device which applies a constant load to the pulley, the pulley 16 can be moved towards or away from the stress compensating device 14 in `order to regulate the tension applied yto the wire 12. The application of this load -on the pulley 16 acts to tension the wire 12 and results in a balancing of the reaction due to the tension in the stressing wire `and leads to a reduction in power required to operate the system.

The stress tensioning device as shown in FIGURE 2 comprises a pair of brackets 18 resiliently loaded by loading me-mbers 18a 'and each of =which brackets 18 carries a rubber-tyred roller 19 adapted to be urged by the loading on the brackets 18 into frictional engagement with the side faces of the hardened concrete beam 9 after its emergence from the curing tunnel 8. Each rubber roller 19 carries a depending spindle 20 connected to the roller 19 through a flexible coupling 21, the spindle 2t) extending downwardly lthrough a hollow capstan 22 before being connected through a second flexible coupling 23 to a gear wheel 24 carried on the lower end of the spindle 20. Each of the gear wheels 24 is in mesh'with a pair of planet wheels 25 mounted on vertical Vstub shafts 26 each of which shafts 26 carries at its upper end a second pair of planet wheels 27 in mesh with a gear wheel 28 secured to the lower end of each oapstan 22. The lower ends of the shafts 26 are mounted in one of a pair of meshing helically-toothed drive wheels 29 one of which is in driving relationship with an electric motor 30. On operation of the electric motor 30 the drive wheels 29 are rotated relative to the gear wheels 24 to cause rotation of the planet wheels 25 and 27 thereby rotating the gear wheels 28 secured to the capstans 22 to effect relative movement between the latter and the drive wheels 29. Otherwise the drive Wheels 29 and capstans 22 are effectively locked to each other and rotate in synchronism.

The motor 30 is operated when for example, due either to wear on therubber rollers 19 or slip, more wire is being fed into the moulding section of the apparatus than is required by the concrete being produced. The motor is controlled by an electrical contact actuated by the position of the piston and cylinder device 17. If more wire is-being fed in than is required the constant load device constituted by the piston and cylinder 17 is automatically operated to cause the pulley 16 to be moved further away from the stress compensating device 14 to take up the slack in the wire. Such movement of the piston and cylinder device 17 is transmitted to the motor 30 of the stress compensating device to cause rotation of the capstans 22 at such a speed and such a direction as to compensate for the overfeeding of the wire.

The capstans 22 are provided with grooves (not shown) on their surface to provide guideways for the wire and as shown in FIGURE 3 the vertical axes of the capstans 22 are canted relative to each other so as to avoid the wire fouling against itself since it is wound round the capstans in gure of eight formation to an extent sufcient to ensure there is no slip. Also, the capstans 22 are of reducing diameter from top Vto bottom and since the Wire isV fed on to each capstan at its lower end, this feature together with the relative canting of the axes ensures that the wire is fed across to a new position on each capstan lin turn and that the wire is fed upwardly on the capstans.

In an alternative formof compensating device as illustrated in FIGURE 4, like parts are designated by the same reference numerals as in the embodiment shown in FIG- URE 3. In .the arrangement of FIGURE 4 the spindles 20 from the rubber-tyred rollers 19 are directly connected to a pair of relatively canted capstans 22 and the wire 12 fed to the capstans 22 from a stock coil 13 is fed through a pair of motor-driven rolls 31. The diameter of the capstans 22 in this case is less than the diameter of the rollers 19 by an amount sufficient to ensure that, if there was no slip on the capstans, the wire 12 is underfed to the rate at which the hardened concrete is fed out thereby providing a prestressed condition to the Wire 12.

In a manner similar to the arrangement of FIGURE 3, the Vrolls 31 .are controlled electrically by an electrical contact actuated by the position of the piston and cylinder device 17. In this way if wire is being overfed or underfed to the stress bed, this causes a corresponding rnovement in the pulley 17 due to the piston and cylinder device. This movement is transmitted to the motor driving the rolls 31 to decrease or increase` respectively the rate of feed of the wire to the capstans 22.

In operation -of the apparatus as shown in the drawings, concrete in `green form is fed through an extrusion machine (not shown) located in the moulding section of the stress bed to surround one or more wires 12 held under tension above the bed and passing through the moulds. By means ofthe endless belt 7 (FIGURE 1) the moulded concrete length together with prestressed wire is continuously moved along the length of the bed to be passed through the curing tunnel 8.4 On emerging from the tunnel 8, the hardened concrete is tested for hardness by the testing device 10 before the continuous length of concrete is severed into sections as desired by the flying saw 11. It willbe readily apparent that instead of the concrete in green form being passed through an extrusion machine located at the moulding section land the lresultant continuous extruded length of prestressedV concrete being .cut into sections by the ying saw 11, the

green-concrete can `be passed into individual moulds at the moulding section and the Wires between adjacent moulds cut by the saw 11.

During the above-described process. the prestressing wire 12 is being continuously fed from the stock coil 13, over the stress compensating device 14, throughthe pre-treatment tunnel 15, over the pulley 16 before passing to the moulding section.

Although in the above-described embodiments a constant load is applied to the pulley 16 through a piston and cylinder device, it will be -apparent that this load can be applied by any other suitable means e.g.` by means of a suspended Weight.

Also although for simplicity only one stressing Wire 12 has been referred to in the above-described embodiments,

` it will be apparent that any convenient number of wires can be fed to Vthe moulding section 6 in like manner.

By means of the present invention, an arrangement is obtained in which the prestressing loads in the reinforcing wire can be nearly balanced since the reaction of the prestressing force is taken lback through the prestressing wire and not through the formed concrete in which the tensioned wire is incorporated the approximate balance is achieved since the reaction force is transferred through i 1. ApparatusV for making prestressed `concrete comi prising a stress bed on-to which unhardened concrete is adapted to be fed, means for continuously feeding stressing wire over said ibed so as to be surrounded by `said concrete and embedded rtherein Awhen the concrete `has hardened, means for continuously applying a wire-tensioning load t-o said wire whereby the wire is maintained in a tensioned condition, and a fixed stress-compensating device included Ain said load-applying means and through which the wire is fed before passing to a movable member having a constant xloa-d applied thereto, said member.

be slidable `relative to said stress-compensating device runder the influence of said load to maintain constantly the wireunder a given tension so Ithat the reaction in`- duced by the tension in the .prestressing wire is transferred bythe stress-compensating device to act in an opposite direetion on the hardened concrete.

2. Apparatus as claimed in claim 1, in which -the stress bed comprises a rolller conveyor having a driven endless conveyor at its forward end, Ithe endless conveyor serving to -advance the concrete to be formed along 4the stressr bed.

3. Apparatus as claimed in'clairn 1, comprising a curing tunnel through which :the formed concrete in green n form and having the stressing wire embedded'therein is adapted to he passed during its passage along -the stress bed.

4. Apparatus as claimed in claim 1, comprising means for pre-treating the stressing wire prior to being incorporated :in the concrete by heating the Wire to a suihcient extent to cause acceleration of the molecular deforma-tion which occurs due to the wires being maintained under tension.

5. Apparatus as claimed in claim 4, in which the wire pre-treating means comprises` a heating tunnel located below lthe stress bed, a xed compensating device through which |the wire is fed before passing to a movable member having a constant load applied thereto, said member being slidable relative said stress-'compensating device under the influence of said load to maintain constantly the wire under a Vgiven Itension so that the reaction induced by the tension in the prestressng wire is transferred by the stress-compensating device .to act in an opposite direction on the hardened concrete.

6. Apparatus .as claimed in claim 1, in which .the movable membery comprises a pulley mounted on a slidable axis.

7. Apparatus as claimed in claim 6, in which the constant load is applied to the movable member by means of a piston and cylinder device. f

8. Apparatus as claimed in claim 1, in which the stresscompensating device comprises capstan means around which the wire :is fed, said capstan means being adapted to feed the wire at .a rate governed by the rate of produc-1 tion of prestressed hardened concrete from the apparatus.

9. Apparatus as cl-aimed in claim 8, in which the cap-` wire, the rollers also serving to apply a force to the hardi enevd concrete in :its direc-tion of ftravel through the ap.

paratus which balances the reaction force induced by the 1 tension in 'the prestressin-g wire.

10. Apparatus as claimed in claim .1, comprising electrical means whereby movement of the movable member due to `overfeeding or underfeeding of ythe wire causes actuation of the stress-'compensating device to compensate for the overfeeding or underfeeding.

Y 11. Apparatus as claimed in claim 8, in which the capstan means comprises a pair of cio-operating c-apstans around which .the wire is fed in gure of eight formation.

12. Apparatus .as claimed :in claim I111, in which the capstans are of increasing diameter from top lto boft-tom and .their kaxes of rotation are :canted relative to each other to prevent fouling of adjacent -runs of wire extending between the capstans.

References Cited by the Examiner UNITED STATES PATENTS Rae 25--118 Schroder et al. 25--118 Ros 25-11-8 Crom 25-118 Kirchner 25-118 Gerwick 25-118 10 J. SPENCER OVERHOLSER, Primm Examiner.

G. A. KAP, Assistant Examiner. 

1. APPARATUS FOR MAKING PRESTRESSED CONCRETE COMPRISING A STRESS BED ON TO WHICH UNHARDENED CONCRETE IS ADAPTED TO BE FED, MEANS FOR CONTINUOSULY FEEDING STRESSING WIRE OVER SAID BED SO AS TO BE SURROUNDING BY SAID CONCRETE AND EMBEDDED THEREIN WHEN THE CONCRETE HAS HARDENED, MEANS FOR CONTINUOUSLY APPLYING A WIRE-TENSIONING LOAD TO SAID WIRE WHEREBY THE WIRE IS MAINTAINED IN A TENSIONED CONDITION, AND A FIXED STRESS-COMPENSATING DEVICE INCLUDED IN SAID LOAD-APPLYING MEANS AND THROUGH WHICH THE WIRE IS FED BEFORE PASSING TO A MOVABLE MEMBER HAVING A CONSTANT LOAD APPLIED THERETO, SAID MEMBER BE SLIDABLE RELATIVE TO SAID STRESS-COMPENSATING DEVICE UNDER THE INFLUENCE OF SAID LOAD TO MAINTAIN CONSTANTLY THE WIRE UNDER A GIVEN TENSION SO THAT THE REACTION INDUCED BY THE TENSION IN THE PRESTRESSING WIRE IS TRANSFERRED BY THE STRESS-COMPENSATING DEVICE TO ACT IN AN OPPOSITE DIRECTION ON THE HARDENED CONCRETE. 